The importance of Soil pH
Soil pH is a basic fundamental to growing a crop. If the pH isn’t right then you lose the availabilty of nutrients. eg, at high pH, phosphorus, Boron and Manganese become less available, and at low pH Molybdenum is less available. There are also different diseases associated with high and low pH.
The Optimum pH for mineral soil is 6.5 when continuous arable cropping (a rotation of cereals potatoes oil seed rape, beans, sugar beet. No specific order), and 6.0 for grassland.
The Optimum pH for Peaty Soil (high in organic matter >20%) is 5.8 for continuous arable cropping and 5.5 for grassland.
The table below shows you the nutrient availability at different pH levels.
Nutrient Index’:
A Basic soil analysis will give you a pH result and Mg, P, and K indices.
The target indices are:
Magnesium – 2 Phosphorus – 2 Potassium – 2-
This highlights the importance of having your soils tested. If you don’t know what nutrients are in your land, then you could be putting fertilisers on unnecessarily, and essentially wasting money. Regarding Phosphorus, over 60% of soils tested were between index 2 and 3 on arable land and 55% on Grassland, therefore there would be no need to put it on.
What is Organic Matter ?
Organic matter is the vast array of carbon-based compounds in soil. Originally created by plants, microbes and other organisms, these compounds play a variety of roles in nutrient, water, and biological cycles. It takes a long time to build up organic matter, you would be doing well if you got up to 10% organic matter in 10 years on an arable system. In grassland it would be slightly quicker as the soil isn’t interrupted.
There is a lot of focus today around building your organic matter and essentially having a healthier soil, this can be done in lots of different ways, here are some common sources of Organic Matter:
- Farmyard manures and slurries
- Poultry litter
- Incorporated crop debris
- Composts
- Anaerobic Digester, Digestate (essentially crops put into a big stew to make energy and digestate is the waste product, but useful to crops)
- Green manures
- Long term grass and leys
As you can see the tables show 34% about 10% organic matter in grass, this is because the land isn’t interrupted. If you plough land and reduce the organic matter.
A very big point to get across from all the tables is how low the Sulphur levels are. When Nitrogen and Sulphur are applied together it increases the plants nutrient use efficiency. Sulphur is vital for building protein. And trials data shows you will get a better return on investment.
Below are bar graphs for Arable and Grassland regarding soil data from Autumn 2023.
Arable Observations
- pH levels - 42.8% below optimum pH range for arable crops
- Most nutrient levels are good apart from sulphur which is well-known as deficient in the soil - 96.5% below sufficient levels
- 22.7% soils are below target index for P and 25% below target index for K
- 52.4% of soils below 5% OM level - lower organic matters mean lower nutrient retention
Grassland Observations
- 41.5% of samples below optimum soil pH – implications for nutrient use efficiency (soil phosphate availability, soil organic matter mineralisation rates), red and white clover persistency
- With 35% of soil samples above the optimum soil P index and 35% below the optimum, significant benefits for some to reduce phosphate applications which could save money, while the other 35% with below optimum soil P are going to have poorer response to N, particularly in spring.
- Most significant of all, nearly 45% of samples have low soil K. This impacts grass growth, particularly silage yields. This is where a nutrient management plan can reap dividends, allowing organic manures to be used strategically to improve grass yields while correcting poor soil fertility.
Soil analysis provides fundamental knowledge on the chemical, physical and biological status of a soil. This information is used to manage the soil and to develop an effective Nutrient Management Plan that optimises crop production. For further information on Soil testing and analysis please visit our page here.
